Retatrutide Weight Loss Trial Reports 18.8% Loss in Diabetes

Results from the TRIUMPH-2 Phase III Trial

The Phase III TRIUMPH-2 clinical trial evaluated retatrutide in 1,152 adults living with both obesity and type 2 diabetes. The study was published in The Lancet and investigated weekly subcutaneous doses over an 80-week period. Eli Lilly developed the drug to treat obesity and glycemic control concurrently.

Participants assigned to the highest weekly dose of 12 mg lost an average of 18.8% of their body weight. That change equaled roughly 20.7 kg, or about 45.5 pounds. In contrast, participants in the placebo group lost an average of 5.1% across the same period.

How the Triple Receptor Agonist Functions

Retatrutide activates three separate metabolic hormone receptors at the same time. Older treatments such as semaglutide stimulate glucagon-like peptide-1 (GLP-1) receptors alone, while tirzepatide stimulates both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptors.

The experimental drug combines GLP-1 and GIP activity with glucagon receptor agonism. GLP-1 lowers blood sugar and promotes satiety, while GIP strengthens insulin release and helps lower body weight. The addition of glucagon receptor activation increases metabolic rate and energy expenditure, which causes the body to burn more calories.

Dose Responses and Cardiometabolic Markers

Weight reduction and glycemic control improved across all three tested doses of retatrutide. Over 80 weeks, participants taking 4 mg, 9 mg, and 12 mg lost an average of 11.9%, 16.8%, and 18.8% of their starting weight. Among volunteers with a baseline body mass index (BMI) of 35 or higher, the 12 mg dose produced an average loss of 21.9%.

Blood sugar control also improved throughout the intervention. Retatrutide decreased hemoglobin A1c (HbA1c) by 1.4 to 1.5 percentage points, compared to a reduction of 0.45 percentage points in the placebo group. Participants also recorded reductions in systolic blood pressure, waist circumference, and circulating triglyceride levels.

• Average weight loss reached 11.9% on 4 mg weekly.
• Average weight loss reached 16.8% on 9 mg weekly.
• Average weight loss reached 18.8% on 12 mg weekly.

Context for Diabetes Management and Obesity Care

People with type 2 diabetes generally encounter greater biological resistance to weight reduction than individuals without diabetes. Earlier clinical trials using single or dual incretin agonists rarely recorded average weight loss above 15% in patients with diabetes.

The TRIUMPH-2 trial demonstrated larger shifts across multiple response thresholds. At the 12 mg dose, 75% of participants lost at least 10% of their body weight. Nearly one-third of the participants on that dose lost 25% or more, an outcome that historically required bariatric surgery. Modest weight reductions of 5 to 10% are known to lower systolic blood pressure and improve high-density lipoprotein cholesterol levels.

Trial Design and Current Regulatory Status

The trial ran as a randomized, double-blind, placebo-controlled investigation. Neither the participants nor the clinical investigators knew who received active retatrutide or placebo injections. To improve tolerability, dosing began at 2 mg weekly and increased in 4-week increments until participants reached their target assignment.

Retatrutide remains an investigational medication that has not received approval from the Food and Drug Administration (FDA) or international health authorities. Individuals seeking changes to their current diabetes regimen should talk to their clinician about approved medical options while clinical evaluation of retatrutide continues.